Chemical vapor deposition (CVD) methods, such as, atomic layer deposition (ALD) methods, are often used in semiconductor processing and other industrial applications to form thin layers of materials. One consideration in selecting a deposition method is the process time to form a desired layer. Further, the quality of a product produced by a deposition method can be important. Along with an increasing need to reduce processing costs, a related desire exists to reduce process time while improving or maintaining product quality.
Speaking generally of ALD, a substrate is exposed to a first precursor material that is chemisorbed onto the substrate. The first precursor material is purged from the deposition chamber and a second precursor is chemisorbed onto the first precursor material on the substrate. Theoretically, the chemisorption of each precursor material is self limiting and the deposited material is formed one monolayer (1 atom thick) at a time. In practice, the ideal theoretical deposition is often not achieved or may be intentionally altered.
One potential cause for a deviation from ideal conditions is the simultaneous presence of the first precursor and the second precursor somewhere in a deposition apparatus other than on the substrate. For example, failure to completely purge one of the precursors from a deposition chamber may cause unwanted deposition on chamber components when the other precursor is introduced. Unwanted mixing of precursors can be a leading cause of particulate formation and product contamination in ALD.
Accordingly, the need to improve product quality and minimize down time for cleaning provides a motivation for careful purging practices. Unfortunately, carefully purging increases process time and accompanying process costs.